In analog integrated circuits, when a reference voltage not dependent on the temperature and power source voltage was used, a reference voltage circuit called a “bandgap circuit” was used. Mounting together with digital circuits is easy, so even in important CMOS analog integrated circuits, bandgap circuits are being widely used as stable reference voltage circuits.
In a related bandgap circuit, the potential of a forward-biased PN junction and a voltage proportional to the absolute temperature (T) (in general, called PTAT) are added to obtain a reference voltage not dependent on the temperature. Various types of such circuits are provided.
It is known that, if approximating the potential of the PN junction by a linear equation or within the range able to be approximated by a linear equation, the potential of the forward-biased PN junction is the complementary-to-absolute temperature (CTAT). Further, it is known that by adding a suitable PTAT voltage to the potential of this forward-biased PN junction, a reference voltage substantially not dependent on temperature is obtained.
Incidentally, in the past, various techniques are proposed for adjusting the value of the VBGR.
Patent Document 1: Japanese National Publication of International Patent Application No. 2004-514230
Patent Document 2: Japanese Laid-open Patent Publication No. H08-018353
Patent Document 3: Japanese Laid-open Patent Publication No. 2005-182113
Patent Document 4 U.S. Pat. No. 5,325,045